copy 2

Question 1

How much cholestrol is synthesized in the liver on avergae per day?

Answer 1

1/g per day

Question 2

What is the general outline of the 4 steps of cholestrol synthesis?

Answer 2

SI: Forms HMG-CoA from Acetyl CoA

SII: Convert from C6 to C5 intermediate. Forms activated 5 carbon intermediates (isoprenoids)

SIII: Six isoprenoids form squalene

SIV: Cyclization of squalene
squalene + O2 form cholesterol

Question 3

What is the rate limiting step in cholestrol synthesis?

Answer 3

HMG-CoA reductase.

HMG-CoA –> mevalonic acid (C6)

Question 4

What are the three different regulatory mechanisims involved in the regulation of HMG-CoA reductase?

Answer 4

1. phosphorylation by cAMP-dependent protein kinases inactivates the reductase.
2. Half life of about three hours, the amount of cholestrol effects the half life
3. Gene expression the amount of cholestrol effects the mRNA.

Question 5

How can the phosphorylation of HMG-CoA reductase be reversed?

Answer 5

2 specific phosphatases.

Question 6

What hormone induces phosphatases for the activation of HMG-CoA reductase?

Answer 6

Insulin

Question 7

Does the fed or fasted state promote cholestrol synthesis?

Answer 7

Fed

Question 8

What hormone induces adenyl cyclase for the inhibtion of HMG-CoA reductase?

Answer 8

Glucagon stimulates adenyl cyclase producing cAMP

cAMP activates protein kinase A
Inactivates HMG-CoA reductase

Question 9

How is the Synthesis of LDL receptors effected by cellular levels of cholestrol?

Answer 9

downregulate LDL receptor synthesis if the cellular levels are high

Question 10

What are the similarties and differences between ACAT and LCAT?

Answer 10

Similar: Both catalyze the formation of Cholestrol Esters.

Difference: ACAT does it for storage of cholestrol

LCAT does it for HDL and transport of cholestrol